This invention relates generally to photographic-reproductive apparatus and methods, and more particularly to an apparatus for producing photographic records of transparencies. The present invention finds particular use in producing photographic records of radiographs, i.e., X-ray films and the like wherein the brightness range of the transparency exceeds that of standard copy materials.
It is important to be able to produce photographic records of images on transparencies such as X-ray films for publication, slide presentations, etc. Such records are produced by photographing the transparency while it is illuminated, and then processing the camera film in appropriate fashion.
A problem arising in the production of such photographic records is that the brightness range of transparencies, i.e., the light transmission range from the darkest to the lightest areas of the transparency image, often exceeds that of standard copy materials, i.e., photographic paper, sometimes by as much as five times or more. When copy materials are chosen to accommodate the entire brightness range of the transparency image, details of the image suffer a loss of contrast and a great deal of information is lost in the photographic record. On the other hand, when copy materials are chosen to preserve detail contrast at midscale of the transparency light transmission range where contrast is the highest, the relatively large brightness range of the transparency image exceeds the acceptance range of the copy material so that a great deal of detail is lost in either the bright areas or the dark areas.
To overcome these drawbacks, attempts have been made to modify or alter the intensity of the illuminating light source to preserve detail and contrast in photographic records of transparencies. Thus, such apparatus utilizing cathode ray tubes (CRT) as the illuminating source vary or modulate the intensity of light generated by the CRT beam, or modulate the velocity of the beam, or both, to reduce the overall contrast of the transparency image so that it can be reproduced on standard copy materials with all detail intact. Others which utilize intensity modulation, while often producing satisfactory results, are somewhat expensive and are slow in operation. Those utilizing velocity modulation or a combination of velocity and intensity modulation are significantly more expensive and combersome.